1. Field of the Invention
The present invention relates to a transmission right managing method which easily manages transmission rights of respective communication devices and reduces a communication traffic amount required for the management in a communication system in which plural communication devices are connected with a transmission line and communication is performed among the plural communication devices, and relates to the communication system.
2. Description of the Related Art
In Example 1 of a conventional communication system in which plural nodes (communication devices) are connected with a transmission line and communication is performed among the plural nodes, the respective nodes judge as to whether or not transmission is performed in the transmission line, and when judging that the communication is not performed, the respective nodes start transmission of transmission data.
In addition, in Example 2 of a conventional communication system, the respective nodes request transmission of a specific node, and the specific node which received the transmission request prioritizes the plural transmission requests received by the respective nodes and gives a transmission right only to the node with the highest priority, and the transmission is started from the node to which the transmission right is given.
Further, Example 3 of the communication system adopts the token passing method where when the node obtaining the transmission right completes the transmission or does not need transmission, the transmission right is transferred to the next node.
However, in Example 1 of the communication system, when the transmission is started simultaneously from the plural nodes, transmission data from the respective nodes conflict with each other in the transmission line, so there arises a problem such that a countermeasure should be taken against the conflict in order to prevent the transmission data from being destroyed.
In addition, Example 2 of the communication system requires data used for requesting transmission from the respective nodes to the specific node and for authorization of the transmission from the specific node to the respective nodes. For this reason, a communication traffic amount is increased. Moreover, in the case where a transmission request is transmitted simultaneously from the plural nodes to a specific node, the transmission requests of the respective nodes conflict with each other in the transmission line, so there arises a problem such that a countermeasure should be taken against the conflict in order to receive all the transmission requests.
Further, in Example 3 of the communication system adopting token passing method, since a transmission right is given regardless of the priority order of the transmission, there arises a problem such that transmission data which should be transmitted very urgently cannot be transmitted quickly.